Sub-freezing temperature presents a significant challenge to the survival of current Li-ion batteries (LIBs) as it leads to low capacity retention and poor cell rechargeability. The electrolyte in commercial LIBs relies too heavily on ethylene carbonate (EC) to produce a stable solid electrolyte interphase (SEI) on graphite (Gr) anodes, but its high melting point (36.4 °C) severely restricts ion transport below 0 °C, causing energy loss and Li plating. Here, a class of EC-free electrolytes that exhibits remarkable low-temperature performance without compromising cell lifespan is reported. It is found that at sub-zero temperatures, EC forms highly resistive SEI that seriously impedes electrode kinetics, whereas EC-free electrolytes create a highly stable, low-impedance SEI through anion decomposition, which boosts capacity retention and eliminates Li plating during charging. Pouch-type LiCoO2 (LCO)|Gr cells with EC-free electrolytes sustain 900 cycles at 25 °C with 1 C charge/discharge, and LiNi0.85 Co0.10 Al0.05 O2 (NCA)|Gr cells last 300 cycles at -15 °C with 0.3 C charge, both among the best-performing in the literature under comparable conditions. Even at -50 °C, the NCA|Gr cell with EC-free electrolytes still delivers 76% of its room-temperature capacity, outperforming EC-based electrolytes.
Keywords: Li plating; Li-ion batteries; ethylene carbonate; low-temperature energy storage; organic electrolytes.
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